Mechanism for adjusting the skew angle of inclination of a printing plate on its plate cylinder

ABSTRACT

A mechanism is described for adjusting the skew angle of inclination of a printing plate engaging the periphery of a plate cylinder, by means of a lever system which adjusts the edges of the printing plate in opposite directions. For this purpose, the two clamping bars are provided on a common baseplate which is lifted at one end prior to releasing the printing plate.

FIELD OF THE INVENTION

The present invention relates generally to a mechanism for adjusting theskew angle of inclination (hereinafter often referred to simply as "theinclination") of a printing plate engaging the periphery of a platecylinder, for the purpose of resister correction, the printing platebeing releasably secured to clamping bars by its heading and trailingedges as considered in the direction of printing cylinder rotation.

More specifically, the invention concerns such a plate registrycorrection mechanism wherein the clamping bars are disposed in anaxis-parallel gap in the periphery of the plate cylinder and areadjustable tangentially for clamping the printing plate. A pivotallymounted lever system also is provided in the cylinder gap and isarticulated to the facing edges of the clamping bars to enable thelatter to be moved in opposite directions and substantially inaxis-parallel relationship for the inclination adjustment. The inventionalso relates to a mechanism for releasing and clamping a printing plateengaging the periphery of a plate cylinder. The leading and trailingedges of the printing plate as considered in the direction of printingrotation are releasably secured to clamping bars disposed in anaxis-parallel gap in the plate cylinder and are adjustable tangentiallyfor the purpose of clamping the printing plate. The clamping bars aremovable where the ends of the printing plate are secured to them for thepurpose of releasing and clamping the same, more particularly inconjunction with an inclination adjustment mechanism.

BACKGROUND OF THE INVENTION

Mechanisms of this kind are described more particularly in EP 232730-A2. Pivotal levers are provided at the two axial ends of thecylinder gap for the inclination adjustment and are connected in anarticulated manner to the edges of the printing plate, their pivotshafts fixed on the cylinder being disposed eccentrically with respectto the gap. To release or clamp the printing plate on the plate cylinderthe clamping bars can be tilted about an axis-parallel axis.

However, it is not possible to obtain perfect inclination adjustment forresister correction with this known mechanism, because the pivot axes ofthe lever system are not situated in the center of the cylinder gap.Moreover, the mechanism described in the said patent for releasing andclamping the printing plate is of complicated construction because notonly are pivot bearings necessary for the two clamping bars, but alsocare must be taken to ensure that the two clamping bars are pivoted insynchronism and opposite directions.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention obviates foregoing disadvantages. The primary aimof the invention is to devise the mechanism such so that accurateadjustment of the inclination of the printing plate is possible withminimum complexity in terms of construction and with the minimum numberof operations.

To solve this problem, the invention is characterised in that the twoclamping bars are disposed on a common baseplate and displaceablerelatively thereto, in that the lever system is mounted pivotally on thebaseplate centrally between the two points of articulation of the leversystem, in that the baseplate is mounted at one axial end to bepivotable in the tangential and radial directions with a substantiallycentral arrangement of the pivot mounting with respect to the cylindergap, and in that the baseplate is adjustable radially at the other axialend.

Since the components forming the inclination adjustment mechanism aredisposed together with the clamping bars on a common baseplate, anappropriate pivoting movement of the baseplate enables the printingplate engaging the plate cylinder to be released so that it restsloosely on the periphery of the plate cylinder and can be displacedrelatively thereto without difficulty. Displacement of the printingplate is by means of the lever system and the resulting inclinationadjustment is very accurate, because the pivot point of the leversystem--unlike the prior art indicated hereinbefore--is disposedcentrally between the two points of articulation of the lever system atthe edges of the printing plate.

Pivoting of the lever system is achieved in a simple manner in terms ofconstruction in that an adjustment spindle engages the lever system, thespindle exerting a force substantially tangentially on the lever system.This arrangement also ensures that the force is transmitted with optimumlever arms.

After the inclination has been adjusted it may be found that there is astill a slight correction required to correct the register, possiblyeven after repeated inclination adjustments, as described above, eachchecked by means of printing proofs with the adjusted plate. For thisreason, in the preferred embodiment of the invention, a fine adjustmentis provided for one of the clamping bars in the axial direction, bymeans of which any remaining register errors can be compensated for.

Starting from a mechanism for releasing and clamping a printing plateengaging the periphery of a plate cylinder, a further object of theinvention is to arrange the mechanism so that release and clamping ofthe printing plate is possible in a simple manner in terms ofconstruction.

Accordingly, the invention is characterised in that the two clampingbars are disposed on a common baseplate and are displaceable relativelythereto, said baseplate being adjustable radially at least at one end.

In carrying out this aspect of the invention, use is made or thesurprising finding that lifting of the baseplate and, with it, the twoclamping bars at just one axial end of the cylinder gap, is sufficientto release the previously clamped printing plate. In this liftingmovement, in fact, the end zones of the printing plate which are bent inthe tangential direction in the clamped condition are stretched and thisstretch is sufficient to release the printing plate from the platecylinder so that the printing plate can be displaced relatively to theplate cylinder periphery, preferably for the above-described inclinationadjustment for register correction.

For this purpose, the baseplate can be lifted appropriately at the twoaxial ends. However, it is sufficient for it to be lifted at just oneend. In this preferred embodiment the baseplate is pivotally mounted atits other axial end.

The invention is explained in detail below with reference to anexemplified embodiment which shows other important features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic plan view of a plate cylinder gap showing theessential components of the mechanism according to the invention inorder to explain the principle;

FIG. 2 is a cross-section through FIG. 1, substantially as seen alongline 2--2, showing other details of the invention;

FIG. 3 is also a cross-section through FIG. 1, substantially as seenalong line 3--3, additionally showing the height adjustment spindle andthe inclination adjustment spindle of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The drawing illustrate a plate cylinder 1 having an axial gap 2. Lateralshoulders 3 are formed in the gap and support a baseplate 4. Edge strips5 are rigidly connected to the tangential ends of the baseplate.Clamping screws 6 are provided and are screwed into screwthreads ofclamping bars 7. The clamping screws are fixed in the edge strips 5 sothat the tangential position can be adjusted in the direction of thedouble arrow 8 of the clamping bars in FIG. 2, by means of the clampingscrews.

Clamping flaps 9 co-operate with the clamping bars 7 so that the leadingand trailing edges 34 and 35 of a printing plate 36 can be clampedbetween the actual clamping bars and their clamping flaps. The clampingflaps are moved by means of their clamping bars. (FIG. 3 omits the headof the right-hand clamping screw 6 in order to simplify the drawing. )

A lever system 10 (see FIG. 1) is secured to the baseplate 4 so as to berotatable about a spindle 11 which is on the center-line 12 of the gap2. Rollers 13, 14, 15 are fixed to the lever system, the rollers 13, 14engaging in slots 16 in the clamping bars 7 while the roller 15 issituated between flanges 17 of an adjustment spindle 18.

The baseplate 4 can be moved in the radial direction at one axial end,i.e. can be lifted and lowered. For this purpose, a height adjustmentspindle shown at reference 19 in FIG. 1 is provided, and is shown indetail in FIG. 3. It will be seen from this that the spindle 19 isscrewed into a tapped bore 20 in the plate cylinder. On rotation of theadjustment spindle 19, the baseplate 4 is moved up or down in thedirection of the arrow 22 by way of a locking ring 21, and with it theclamping bars and the other components fixed on the baseplate.

FIG. 3 also shows that the adjustment spindle 19 can either be rotatedmanually, for which purpose a polygonal key can be applied to thespindle at reference 23, or it can be moved by motor, for example, byway of a gearwheel or sprocket wheel 24.

The lateral adjustment spindle 18 can also be moved manually or bymotor, for which purpose FIG. 3 again shows a gearwheel or sprocketwheel 25.

At the other axial end the baseplate 4 is mounted rotatably andpivotally on the plate cylinder at reference 26. This mounting 26 (seeFIG. 1) is, for example, in the form of a ball bearing, the baseplatebeing laterally pivotable in accordance with the adjustment or thespindle 18 and vertically pivotable in accordance with the adjustment ofthe spindle 19.

To incline the printing plate 36, the latter is first released, it beingassumed that the printing plate 36 is clamped fast by its edges by meansof the clamping bars 7, 9. To release the printing plate, the heightadjustment spindle 19 is actuated, so that the associated end of thebaseplate is moved upwards in the direction of arrow 22. The printingplate 36, which was bent out of its circular form in the direction of atangential over the edges 27 of the plate cylinder on the transitionfrom the periphery of the latter to the gap, is thus stretched and theprinting plate material thus freed enables the printing plate to be soreleased from the periphery from the plate cylinder that the printingplate can now be moved relatively to the plate cylinder.

The spindle 18 is now rotated so that the lever system 10 is moved tothe right or left in the direction of arrow 28 in FIG. 1 by way of theroller 15. The resulting pivoting of the lever system 10 about the axis11 results in the spaced apart clamping bars 7 and their associatedclamping flaps 9 being moved in opposite directions axially, i.e. in thedirection of the double arrow 29 in FIG. 1. This is the requiredinclination adjustment. The printer now prints a proof, by rotating thecylinder 1 and attached plate 36 in the direction of printing rotation,shown by arrow 38 in FIG. 2, and if register is not yet achieved he willadjust to one or other additional inclined positions, as describedabove, until register is achieved. The height adjustment spindle 19 isthen actuated to bring the baseplate 4 back to bear on the shoulders 3end thus fix it on the cylinder 1. The printing plate 36 is now alsoclamped fast on the plate cylinder and accurate-register printing ispossible.

It may be necessary for fine correction to be carried out beforehand,for which purpose the slot 16 associated with the roller 13 is formed ina block 30 which has a tapped bore in which an adjustment screw 31engages by its screwthreaded end. When the adjustment screw is turned,the block is finely adjusted accordingly in the axial direction (arrow29) and this displacement acts by way or the lever system 10 to producea corresponding displacement of the other clamping bar in the oppositedirection.

It will therefore be seen that the mechanism according to the inventionis simple to operate and gives a very accurate inclination adjustment.The printing plate 36 has to be released--by means of the heightadjustment spindle 19--end the necessary inclination adjustment can thenbe effected by actuating the side adjustment spindle 18. A peripheralcorrection is simultaneously achieved as a result.

With the described inclination adjustment or inclination correction,there may be peripheral and lateral shifts, but they can be compensatedfor by means of the peripheral and side resister control on theassociated sheet-fed printing machine.

It is therefore important that once the plate 36 has been clamped inposition by the clamping bars 7 it can remain clamped thereon during theinclination adjustment. If the printing plate were to be frequentlyreleased end clamped at the clamping bars, it might be damaged. Thisapplies particularly to the very thin printing plates customary today.These disadvantages are obviated by the invention.

The mechanism described can also be varied in respect of itsconstructional details. For example, a screwthreaded nut can be screwedon to the lateral adjustment spindle 18 and be pivotally connected tothe lever system 10 so that when the spindle is rotated the nut travelsalong the spindle end thus shifts the clamping strips. The lever system10 is denoted by a circle in FIG. 1 but it may have other forms, forexample a three-armed lever.

FIG. 3 also shows that the adjustment spindle 18 engages by ascrewthreaded end in a co-acting thread of a screwthreaded member 32fixed in a through hole in the associated edge strip 5. At the other endthe adjustment spindle 18 extends through a through hole in the otheredge strip 5.

It should be noted that FIG. 1 is not a true-to-scale drawing; thedistance between the adjustment system comprising the lever system 10and the height adjustment spindle 19 and the mounting 26 is larger thanshown in FIG. 1, because the spindle 19 and the mounting 26 are situatednear the axial ends of the cylinder gap 2.

In the released position--the baseplate lifted by means of the spindle19--the clamping bars can be shifted in the direction of arrow 29. Theclamping screws 6 do not obstruct this movement because they are movedtogether with the clamping bars. In addition, the displacement travel isgenerally only a few millimeters.

FIG. 1 also shows that the adjustment spindle 18 bears against the wallsof the gap 2 by its points. Nevertheless, the roller 15 can be moved inthe direction of arrow 28 because on rotation of the adjustment spindle18 the entire clamping mechanism is shifted in the gap. This shift isalso only a few millimeters.

I claim:
 1. A mechanism for adjusting the skew angle of inclination of aprinting plate mounted on the periphery of a rotatable plate cylinder ina printing press for the purpose of register connection, wherein theplate cylinder has an axis-parallel gap in the periphery thereof, saidprinting plate has leading and trailing edges with respect to thedirection of printing rotation of the plate cylinder, and a pair ofsubstantially axis-parallel clamping bars disposed in the gap formovement substantially tangentially with respect to the plate cylinderperiphery for releasably clamping the leading and trailing edges of theprinting plate to tension the plate on the periphery of the platecylinder, said inclination-adjusting mechanism comprising, incombination,a base plate disposed in said gap and means for supportingsaid clamping bars for axial and tangential movement thereon, means forradially raising and lowering at least one axial end of said base platein said gap for loosening and tightening the printing plate on theperiphery of the plate cylinder, an articulated linkage includingseparate lever arms pivotally mounted substantially centrally on saidbase plate and operatively connected to said clamping bars for movingsaid clamping bars substantially axially with respect to said base plateand substantially oppositely with respect to one another for adjustingthe skew angle of inclination of the printing plate on the periphery ofthe plate cylinder, and means including a common lever arm for pivotingsaid separate lever arms of said articulated linkage while the printingplate is loosened on the periphery of the plate cylinder for adjustingthe skew angle of inclination of the plate thereon.
 2. An adjustingmechanism according to claim 1 wherein said means for pivoting saidcommon arm of said articulated linkage includes an adjustment spindledisposed to exert a substantially tangential pivoting force on saidcommon arm.
 3. An adjusting mechanism according to either claim 1 or 2wherein a registry adjustment means including a threaded adjustmentblock and a fine adjustment screw are interposed between one of saidseparate lever arms and one of said clamping bars for adjusting saidoperative connection therebetween.
 4. An adjusting mechanism accordingto either claim 1 or 2 wherein said means for radially raising orlowering said one axial end of said base plate includes a radialadjustment spindle interposed between said one end of said base plateand said gap in said plate cylinder periphery.
 5. An adjustmentmechanism according to claim 4 wherein the other axial end of said baseplate is pivotally mounted in said gap.